Add prototype serialization tests. (#18458)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.IntegrationTests/Tests/PrototypeTests/PrototypeTests.cs

@@ -0,0 +1,52 @@
+using Robust.Shared.Prototypes;
+using Robust.UnitTesting;
+
+namespace Content.IntegrationTests.Tests.PrototypeTests;
+
+public sealed class PrototypeTests
+{
+    /// <summary>
+    /// This test writes all known prototypes as yaml files, then validates that the result is valid yaml.
+    /// Can help prevent instances where prototypes have bad C# default values.
+    /// </summary>
+    [Test]
+    public async Task TestAllPrototypesAreSerializable()
+    {
+        await using var pairTracker = await PoolManager.GetServerClient();
+        var context = new PrototypeSaveTest.TestEntityUidContext();
+        Assert.Multiple(() =>
+        {
+            Validate(pairTracker.Pair.Server, "server", context);
+
+            // TODO fix client serialization
+            //Validate(pairTracker.Pair.Client, "client", context);
+        });
+        await pairTracker.CleanReturnAsync();
+    }
+
+    public void Validate(RobustIntegrationTest.IntegrationInstance instance, string instanceId,
+        PrototypeSaveTest.TestEntityUidContext ctx)
+    {
+        var protoMan = instance.ResolveDependency<IPrototypeManager>();
+        var errors = protoMan.ValidateAllPrototypesSerializable(ctx);
+
+        if (errors.Count == 0)
+            return;
+
+        Assert.Multiple(() =>
+        {
+            foreach (var (kind, ids) in errors)
+            {
+                foreach (var (id, nodes) in ids)
+                {
+                    var msg = $"Error when validating {instanceId} prototype ({kind.Name}, {id}). Errors: \n";
+                    foreach (var errorNode in nodes)
+                    {
+                        msg += $" - {errorNode.ErrorReason}\n";
+                    }
+                    Assert.Fail(msg);
+                }
+            }
+        });
+    }
+}